The rising cost and the coming shortage of automotive fuel makes it an object for the automotive industries to improve the fuel economy of automotive vehicles. Several different improvements in the internal combustion engine technology have been made in order to maximize fuel economy. Among these improvements are different injection technologies, different ignition technologies and turbo-charging of the engine. Another improvement used to reduce fuel consumption is the development of an internal combustion engine capable of shutting down some cylinders when the full power of the engine is not needed (e.g., when cruising on a highway) and where all cylinders are used when more power is needed (e.g., when accelerating or climbing).
An engine using this type of technology is often referred to as a Variable Displacement Engine (VDE). In such an engine, the fuel supply is shut off to the cylinders that are to be shut down. At the same time, as the fuel supply is shut off, the intake valves and exhaust valves of these cylinders may be held opened or closed. With closed valves, the engine will perform an internal compression work that will induce so-called NVH (Noise, Vibration, and Harshness) problems. The magnitude of these problems is dependent on the engine speed. At high engine speeds, the NVH problems are less noticeable, so that the closed valve technology can be used at high engine speeds. At low engine speeds, the closed valve technology is impractical. One problem using open valves is that cold air is pumped into the exhaust system, which influences the three-way conversion of the catalyst in a detrimental way.
A further disadvantage with the VDE engine technology is that the pistons of the shut off cylinders still move, together with the connecting rods and the crank shaft, which in turn results in power loss due to internal friction in the engine. Yet another disadvantage with the VDE engine technology is that the torque fluctuations will increase, with a higher maximum peak torque and more zero torque passages, compared with the same engine running on all cylinders.
Different specialized modifications of multi-cylinder internal combustion engines have been disclosed earlier for achieving various results. The use of two or more separate crank shafts to serve some cylinders relative to the remaining cylinders has been described in U.S. Pat. Nos. 4,170,970, 4,470,379, 5,732,668 and 6,205,972. However, said separate crank shafts generally operate synchronously, and not in a selectively alternating manner to accomplish results other than fuel economy. U.S. Pat. No. 7,080,622 discloses a split engine, wherein the divided crank shaft is provided with an overrun clutch arranged between adjacent bearings. U.S. Pat. No. 4,069,803 discloses a split engine with a crank shaft clutch arrangement located between adjacent bearings. The clutch comprises a hydraulically actuated cone clutch with synchronizing teeth.
These solutions may function for some applications, but they still show some disadvantages. One disadvantage is that additional space between adjacent cylinders is required. Thus, there is room for improvement.